A living body is protected from exogenous matters mainly by immunological responses, and immune systems are constructed by various cells and soluble factors made by the cells. Among them, leukocytes, particularly lymphocytes play a central role. The lymphocytes are classified into two main types called B lymphocytes (hereinafter, referred to as B cells in some cases) and T lymphocytes (hereinafter, referred to as T cells in some cases), and either of them specifically recognizes an antigen, and acts on it to defend a living body.
Most of the T cells are composed of CD4 positive T cells expressing a CD (Cluster of Differentiation) 4 marker and CD8 positive T cells expressing a CD8 marker, at the periphery. Most of the CD4 positive T cells are called helper T cells (hereinafter, referred to as TH), and are involved in assistance of antibody production and inducement of various immunological responses, and are differentiated into a Th1 type and a Th2 type in which the kinds of cytokines produced by antigen stimulation are different from each other. Most of the CD8 positive T cells are differentiated into cytotoxic T cells [Tc: cytotoxic T lymphocytes, also called as killer T cells, hereinafter, referred to as a CTL in some cases] exhibiting cytotoxic activity by antigen stimulation.
As a fourth cancer therapy next to surgical operation, chemotherapy, and radiation therapy, immunotherapy has been drawing attention recently. Since the immunotherapy utilizes the immunological ability originally possessed by human beings, it is said that the physical burden on a patient is smaller as compared with other therapies. The known immunotherapy include a therapy for introducing lymphokine activating cells, NKT cells, a γδT cells, etc. obtained from in vitro induced CTL, peripheral blood lymphocytes by expansion-culturing according to a variety of methods, a dendritic cell transferring therapy and a peptide vaccine therapy expecting in vivo inducement of antigen-specific CTL, a Th1 cell therapy and, further, an immune gene therapy in which a gene from which various effects can be expected is introduced into these cells in vitro, followed by transferring into a body.
Some of cytotoxic T cells (CTL) recognize a complex which is a binding material of a major histocompatibility antigen molecule (MHC molecule, in the case of human beings, called a human leukocyte antigen, hereinafter, abbreviated as an HLA) encoded by a major histocompatibility gene complex (hereinafter, abbreviated as an MHC) and an antigenic peptide, with a specific T cell receptor (hereinafter, abbreviated as a TCR) composed of a heterodimer of an α chain and a β chain, and can damage a cell presenting the complex on its surface.
It is expected to impart cytotoxic activity specific to an objective antigen to a T cell having cytotoxic activity including a CTL by introducing a TCR gene recognizing the objective antigen into the T cell. Based on this expectation, a gene therapy with a TCR gene targeting various antigens such as MART1 (Non-Patent Document 1), gp100 (Non-Patent Document 2) and an mHAG HA-2 antigen (Non-Patent Document 3) have been tried. However, for example, when a TCR gene composed of an α chain and a β chain recognizing an objective antigen is introduced into a T cell, the endogenous TCR α chain and TCR β chain originally expressed by the T cell cause mispairing between a β chain and an α chain of the introduced TCR recognizing the objective antigen. That is, when α′ and β′ are introduced into a cell expressing α and β, each heterodimer of αβ, αβ′, α′β, and α′β′ is formed, thereby causing a problem that TCRs forming a proper heterodimer to recognize the objective antigen are decreased, and a heterodimer recognizing an unexpected antigen may be formed.
As a method for solving this problem, a method of introducing a single-stranded TCR which does not form a heterodimer with an endogenous TCR into a T cell (Non-Patent Document 4), and a method of introducing a chimeric receptor (T-body) with an antibody recognizing an objective antigen into a T cell (Non-Patent Document 5) have been tried. However, since a T cell obtained by these methods have both of an endogenous TCR and an introduced TCR, the T cell may recognize two kinds of antigens. Further, since a recombinant TCR is not a naturally occurring TCR, it is necessary to confirm signal transmission to a T cell, safety, etc. In addition, as another method, there is a method of introducing a β chain and an α chain of a TCR recognizing an objective antigen into a T cell not expressing an α chain and a β chain of a TCR, for example, a T cell (γδ T cell) expressing a γ chain and a δ chain (Non-Patent Document 6). However, a T cell obtained by this method has the same concern as that of the method of using a recombinant TCR.
As illustrated above by the TCR, when a exogenous polypeptide which can be incorporated into an oligomeric protein as a constituent polypeptide is introduced into a cell expressing the protein, there are problems that an oligomeric protein which is not capable of manifesting the desired function and in which an endogenous polypeptide and a exogenous polypeptide are mixed may be formed, or an oligomeric protein manifesting the desired function may be decreased by the competition between an endogenous polypeptide and a exogenous polypeptide.    Non-Patent Document 1: J. Immunol., vol. 163, pp. 507-513 (1999)    Non-Patent Document 2: J. Immunol., vol. 170, pp. 2186-2194 (2003)    Non-Patent Document 3: Blood, vol. 103, pp. 3530-3540 (2003)    Non-Patent Document 4: Gene Therapy, vol. 7, pp. 1369-1377 (2000)    Non-Patent Document 5: J. Clin. Invest., vol. 114, pp. 1774-1781 (2004)    Non-Patent Document 6: Cancer Res., vol. 66, pp. 3331-3337 (2006)